Stress composite sensor and stress measuring device using the same for structure

ABSTRACT

A stress composite sensor has sensor elements each including a base plate having a rectangular configuration and a first main surface and a second main surface opposite the first main surface, a pair of first strain gauges disposed on the first main surface crossing one another, a pair second strain gauges disposed on a the second main surface crossing one another, the first pair of strain gauges and the second pair of strain gauges being symmetrically disposed with respect to a center plane of the base plate; and bridge circuits incorporating the first pair of strain gauges and the second pair of strain gauges. The sensor elements include X-sensor elements for measuring stress in an X-direction, Y-sensor elements for measuring stress in a Y-direction, and Z-sensor elements for measuring stress in a Z-direction. Arithmetic circuits calculate stress from outputs of the bridge circuits. The X-sensor elements have edge portions orthogonally joined to edge portions of the Y-sensor elements to form L-shaped sensor segments and the Z-sensor elements are each edgewise joined to ones of the L-shaped sensor segments orthogonal to the X-sensor elements and the Y-sensor elements thereby forming three plane sensor segments having three contiguous faces of a parallelepiped and to output X-, Y- and Z-direction stress signals. The three plane sensor segments are joined together in a matrix to form one assembled body.

This is a continuation, of application Ser. No. 08/524,858, filed Sept.7, 1995. U.S. Pat. No. 5,723,792

BACKGROUND OF THE INVENTION

The present invention relates to a stress composite sensor and a stressmeasuring device using the same for a structure, for measuring stresses,such as shearing stresses, or shearing strains, produced in a structuresuch as an automobile, airplane, railroad vehicle, crane, robot or thelike.

Methods for measuring stresses, such as shearing stresses, or shearingstrains, produced in a structure such as an automobile, airplane,railroad vehicle, crane, robot or the like, include the photoelasticitymethod, brittle coating method, acoustic method, holographic method andstrain gauge method, of which generally the strain gauge method has beenused most frequently.

Such mechanical quantity sensors are various in kind and easy to handle,but when used for measuring stresses, they have to be equipped withtransducers. Further, in the strain gauge method, the strain gauge issubjected to stresses in every direction and hence analysis is required.

Further, a stress sensor comprising a conventional mechanical quantitysensor such as a strain gauge, when singly used on a structure, receivesgreater amounts of other stresses than the main stress depending uponthe position where it is attached; thus, a plurality of stress sensorshave to be used and such stress sensor has to be attached to the neutralpoint where other stresses than the main stress are not transmitted orreduced, making it necessary to find the neutral point possessed by thestructure and to attach a stress sensor to the neutral point accurately.

SUMMARY OF THE INVENTION

With the above in mind, the present invention provides an arrangementwherein instead of singly using stress sensors (mechanical quantitysensors) comprising strain gauges, a plurality of stress sensors arecomposited or integrated to provide an integral stress composite sensor,which is mounted on a structure such as an automobile whose stresses areto be measured, and X-, Y- and Z-axis direction stress signals obtainedfrom the single-packaged stress composite sensor are selectively used tomeasure stresses.

The present invention includes a plurality of stress sensors or aplurality of rows of stress sensors comprising strain gauges areintegrated by being fixed on the same plane of a base plate atintervals, so that each stress sensor delivers stress signals in onedirection alone or a selected stress sensor delivers stress signals inone direction alone.

The present invention provides stress sensors comprising strain gaugesfixed on the individual surfaces of base plates placed in two mutuallyorthogonal planes and thereby integrated to provide a sensor segment, aplurality of such sensor segments or a plurality of rows of such sensorsegments being connected together or superposed and connected togetherto form an integral body, so that each sensor segment delivers stresssignals in two directions or a selected sensor segment delivers stresssignals in two directions.

The present invention also provides stress sensors comprising straingauges fixed on the individual surfaces of base plates placed in threemutually orthogonal planes and thereby integrated to provide a sensorsegment, a plurality of such sensor segments or a plurality of rows ofsuch sensor segments being connected together or superposed andconnected together to form an integral body, so that each sensor segmentdelivers stress signals in three directions or in selected directions ora selected sensor segment delivers stress signals in three directions.

The present invention further provides a signal processing circuit suchas a bridge circuit of strain gauges or an amplifying circuit integrallyformed on the same base plate as that of a stress composite sensor asdescribed above.

The present invention still further provides for a hole formed in thestress concentration region of a structure whose stresses are to bemeasured and a stress composite sensor being selectively installed, sothat X-axis, X- and Z-axis or X-, Y- and Z-axis direction shearingstrains produced in the structure are selectively measured correspondingto the selected stress composite sensor.

The present invention additionally provides a stress measuring devicefor a structure described above, when shearing strains produced in thestructure are to be sensed, at least one or more necessary sensors orsensor segments of the stress composite sensor being sorted for stressmeasurement.

The present invention yet further provides a stress composite sensor asdescribed above being selectively installed in a hole formed in thestress concentration region of a structure whose stresses are to bemeasured, thereby making it possible to measure stresses in a particulardirection or summed stress signals from a plurality of sorted sensorsegments by means of sorted stress signals in the X- and Y-axis or X-,Y- and Z-axis directions of the structure.

The present invention further still provides a stress composite sensoras described above being installed in a hole formed in the stressconcentration region of a structure whose stresses are to be measured,and the stress sensors in a plurality of selected sensor segments alonein the X-axis, X- and Y-axis or X-, Y- and Z-axis directions of thestructure are employed for sensing and their stress signals areseparated according to the X-, Y- and Z-axis directions, such separatedstress signals being respectively added together to provide stresssignals which are subjected to comparative computation for stressmeasurement.

The present invention also provides in a stress measuring device for astructure described above, when a necessary sensor segment is sorted forstress measurement, a plurality of stress signals of the sensor segmentsalong a stress layer having relatively little mixing of other stressesproduced in the structure being derived and combined for stressmeasurement.

The present invention also in a stress measuring device for a structuredescribed above, stresses in the X- and Z-axis or X-, Y- and Z-axisdirections being sorted to measure stresses in the necessary directions,the resulting stress signals being used as control parameters.

According to the invention, a plurality of stress sensors or a pluralityof rows of stress sensors comprising strain gauges are integrated bybeing fixed on the same base plate, whereby each stress sensor in thesingle package delivers signals in one direction alone or a selectedstress sensor delivers stress signals in one direction alone, and hencestresses in one direction can be measured.

According to the present invention, stress sensors comprising straingauges are fixed on the individual surfaces of base plates placed in twomutually orthogonal planes and thereby integrated to provide a sensorsegment, a plurality of such sensor segments or a plurality of rows ofsuch sensor segments being connected together or superposed andconnected together to form an integral body, so that each sensor segmentin a single package delivers stress signals in two directions or aselected sensor segment delivers stress signals in two directions aloneand hence stresses in two directions can be measured.

According to the present invention, stress sensors comprising straingauges are fixed on the individual axis surfaces of base plates placedin three mutually orthogonal planes and thereby integrated to provide asensor segment, a plurality of such sensor segments or a plurality ofrows of such sensor segments being connected together or superposed andconnected together to form an integral body, so that each sensor segmentin a single package delivers stress signals in three directions or aselected sensor segment delivers stress signals in three directions.Thus, stresses in three directions can be measured.

According to the present invention, a signal processing circuit such asa bridge circuit of strain gauges or an amplifying circuit is integrallyformed on the base plate for the stress sensor or sensor segment; thus,the measuring function can be improved to increase reliability.

According to the present invention, a single-packaged stress compositesensor described in claims 1 through 4 is selectively installed in ahole formed in the stress concentration region of a structure, wherebyX-axis, X- and Z-axis or X-, Y- and Z-axis direction shearing strainsproduced in the structure or 1-, 2- or 3-direction stressescorresponding to the selected stress composite sensor can be selectedand measured.

According to the present invention as described above, when shearingstrains produced in a structure are to be sensed, at least one or morenecessary sensors or sensor segments of the stress composite sensor aresorted for stress measurement, whereby stresses in any desired directionand an amount of change in said stresses can be derived and accuratelymeasured.

According to the present invention as described above, a stresscomposite sensor capable of measuring stresses in a single direction ora plurality of directions is selectively installed in a hole formed inthe stress concentration region of a structure, whereby stresses in aparticular direction or summed stress signals from a plurality of sortedsensor segments can be derived by means of sorted stress signals in theX-axis, X- and Z-axis or X-, Y- and Z-axis directions of the structureand thus stresses can be measured.

According to the present invention as described above, a stresscomposite sensor capable of measuring stresses in a single direction ora plurality of directions is installed in a hole formed in the stressconcentration region of a structure, and a plurality of selected sensorsegments alone in the X-axis, X- and Y-axis or X-, Y- and Z-axisdirections are employed for sensing and their stress signals areseparated according to the X-, Y- and Z-axis directions, such separatedstress signals being respectively added together for comparativecomputation of the resulting stress signals so as to measure stresseswith increased accuracy.

According to the present invention as described above, in a stressmeasuring device for a structure described above, when necessary sensorsegments are sorted for stress measurement, a plurality of stresssignals of the sensor segment along a stress layer having relativelylittle mixing of other stresses produced in the structure are derivedand combined for stress measurement; thus, stresses not influenced bycross talk are easily measured.

According to the present invention as described above, in a stressmeasuring device for a structure described above, stresses in the X- andZ-axis or X-, Y- and Z-axis directions are sorted to measure stresses inthe necessary directions, the resulting stress signals being used ascontrol parameters; thus, it is possible to construct a highly reliablecontrol system adapted to accurately derive stresses in necessarydirections alone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a 1-direction sensor segment;

FIG. 2 is a perspective view of a 1-direction stress composite sensor;

FIG. 3 is a perspective view of a 2-direction sensor segment;

FIG. 4 is a perspective view of a 2-direction stress composite sensor;

FIG. 5 is a perspective view of a laminated 2-direction stress compositesensor;

FIG. 6 is a perspective view of a 3-direction sensor segment;

FIG. 7 is a perspective view of a 3-direction stress composite sensor;

FIG. 8 is a perspective view of a laminated 3-direction stress compositesensor;

FIG. 9 is a view showing an example of signal processing circuit using1-direction sensor elements;

FIG. 10 is a view showing an example of signal processing circuit usingtwo rows of sensor segments connected together;

FIG. 11 is a perspective view showing an example in which a 1-directionstress composite sensor is installed in a hole in an axle of a vehicle;

FIG. 12 is an enlarged view of the region where the stress compositesensor is installed in FIG. 11;

FIG. 13 is a view showing a disk type 1-direction stress compositesensor installed in a hole in an axle of a vehicle;

FIG. 14 is a view showing a plurality of 1-direction stress compositesensors installed in the same hole in an axle of a vehicle;

FIG. 15 is a view showing a 2-direction stress composite sensorinstalled in a hole in an axle;

FIG. 16 is a view showing a 1-direction and 2-direction stress compositesensors installed in the same hole in an axle of a vehicle;

FIG. 17 is a view showing a 3-direction stress composite sensorinstalled in a hole in an axle;

FIG. 18 is a view showing a 2-direction stress composite sensorinstalled in an angular hole in an axle; and

FIG. 19 is a view showing a stress composite sensor installed in a holein an axle and fixed in position by a filler.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

What is shown herein is an example of preferred mode of embodiment andthe scope of the present invention is not limited by embodiments shownherein.

The present invention will now be described with reference toillustrated embodiments showing examples of a stress measuring deviceapplied to a vehicle, particularly an automobile.

FIG. 1 shows an example of the basic arrangement of a 1-direction stresscomposite sensor, wherein strain gauges a, b, c, d formed of metalresistance foil are fixed, in pairs with the two in each pair crossingeach other, on the opposite surfaces of a base plate 1 made of a plasticmaterial such as epoxy resin, metal or silicon material so as to form astress sensor S, which is a sensor element, a plurality of such sensorelements being integrally connected together on the same plane to form asensor segment g; each stress sensor S is used to measure stresses inone direction or a selected sensor segment is used to measure stressesin one direction.

In FIG. 2, a plurality of rows of sensor segments g as shown in FIG. 1are prepared and signal processing circuits G such as bridge circuitsand amplifying circuits are integrally formed on a a common base plate 1into a single package to provide a stress composite sensor P', so thateach stress sensor S in the sensor segments g or the stress sensors S inselected sensor segments g alone are used to measure stresses in onedirection.

FIG. 3 shows an example of the basic arrangement of a 2-direction stresscomposite sensor, wherein sensor elements e1 and e2 which have stresssensors S fixed thereto and which are integrally connected together atright angles to form a sensor segment g', so that stresses in twodirections, X- and Z-axis directions, can be measured.

In FIG. 4, a plurality of the sensor segments g' (in 4 lateral rows and3 longitudinal rows) shown in FIG. 3 are integrally connected togetherto form a 2-direction stress composite sensor P", so that stresses intwo directions can be measured by each sensor element e in the sensorsegments in the X- and Z-axis directions or by the stress sensors S inselected sensor elements e.

In FIG. 5, 2-direction stress composite sensors P" shown in FIG. 4 arelaminated in multilayer (in two layers) and connected together, whereby2-direction stress composite sensors are formed into a single package.

FIG. 6 shows an example of the basic arrangement of a 3-direction stresscomposite sensor, three sensor elements having stress sensors S fixed onbase plates 1 are integrally connected in the three directions of theX-, Y- and Z-axes to form a sensor segment g", so that individualstresses are measured by the individual stress sensors S, wherebystresses in three directions can be measured.

In FIG. 7, a plurality of sensor segments g" (in 4 lateral rows and 3longitudinal rows) as shown in FIG. 6 are integrally connected togetherto form a 3-direction stress composite sensor P'", so that stresses inthree directions can be measured by each sensor element in the sensorsegments in the X-, Y- and Z-axis directions or by the stress sensors inselected sensor elements e.

In FIG. 8, 3-direction stress composite sensors P'" shown in FIG. 7 arelaminated in multilayer (in two layers) and connected together, areformed into a single packaged 3-direction stress composite sensor LP.

The aforesaid 2-direction sensor segment g', 2-direction stresscomposite sensor P", 3-direction sensor segment g" and 3-directionstress composite sensor P'" is producible by semiconductor process ormade of ceramic or is other material, and a signal processing circuit Gsuch as a bridge circuit or amplifying circuit for the stress sensor Sis optionally integrally formed on the same base plate such as a metalbase or semiconductor base into a single package, in the same mannerwith that shown in FIG. 2. Further, in the case where a signalprocessing circuit is to be integrally formed on the base plate 1 of thesensor segment g shown in FIG. 2, the strain gauges a, b, c, d in eachsensor element e together with adjusting resistors r, as shown in FIG.9, constitute bridge circuits, which are connected to arithmeticcircuits A and B through amplifying circuits AP to form a logic circuitL1, the respective outputs from the logic circuits L1--L3 beingconnected to arithmetic circuits C and C' so as to derive stresssignals.

FIG. 10 shows an example of the arrangement of a signal processingcircuit comprising for a 1-direction stress composite sensor comprisingtwo rows of sensor segments g connected together. A signal processingcircuit for 2- and 3-direction stress composite sensors can be formed byapplying the same idea of forming said signal processing circuit for1-direction stress composite sensor.

In addition, strain gauges for the stress sensor S have been shown asusing metal resistance wire strain gauges, but the invention is notlimited thereto and strain gauges based on piezoelectric effect, straingauges based on crystalline structure, and semiconductor strain gaugesare optionally used.

FIG. 11 shows an example of the stress measuring device of the presentinvention applied to an automobile (structure) K, wherein a hole 3 isformed in an axle 2 in the X-axis direction which is the direction oftravel of the vehicle and a stress composite sensor P* capable ofmeasuring stresses in one direction alone or two or three directions isselectively mounted in said hole, thereby constituting the stressmeasuring device. In this case, the friction force F can be measured inthe X-axis direction which is the direction of travel of the vehicle,the transverse force can be measured in the Y-axis direction which isthe transverse direction, and the vertical reaction (vertical load) Ncan be measured in the Z-axis direction which is the vertical direction.

FIG. 12 is an enlarged view of stress measuring means comprising astress composite sensor P1 installed in a hole 3 in an axle 2 formeasuring stresses in one direction alone, as shown in FIG. 2, the saidstress composite sensor P1 being embedded with the longitudinal edge ofits base plate 1 brought into contact with the peripheral wall of thehole 3. If necessary, a filler may be charged into the empty space toprovide a waterproof construction.

In this stress measuring device, each stress sensor S of a plurality ofrows of equispaced coplanar sensor segments g effects sensingcorresponding to shearing strains in the X-axis direction alone producedin the axle 2 to deliver a stress signal; thus, the friction force F canbe measured.

Further, as shown in FIG. 13, a 1-direction stress composite sensor Pmay be made in the form of a disk and if it is installed in a hole 3 inan axle at right angles with the X-axis direction, it delivers a stresssignal in the vertical direction alone to make it possible to measurethe vertical load N.

FIG. 14 shows an example of a stress measuring device comprising three1-direction stress composite sensors P1, P2 and P3 installed atintervals in a hole 3 in an axle 2. In this case, the main sensor P1 andsub-sensors P2 and P3 effect sensing in the X-axis direction alonecorresponding to shearing strains formed in axle 2 to deliver stresssignals, of which 1-direction stress signals optimum for use as brakecontrol parameters are selected to measure the friction force F.

If the 2-direction stress composite sensor P" shown in FIGS. 4 and 5 isinstalled in the hole 3 in the axle 2 to constitute a stress measuringdevice, the stress sensors S of many sensor elements effect sensing todeliver stress signals corresponding to shearing strains produced in twodirections, the X- and Z-axis directions, in the axle 2, and selectedout of said stress signals are those stress signals in the X- and Z-axisdirections which are optimum for use as brake control parameters toenable measurement of the friction force F and vertical load N, and theroad surface friction coefficient μ can be easily obtained byarithmetically processing their output values.

If the 3-direction stress composite sensor P'" shown in FIGS. 7 and 8 isinstalled in the hole 3 in the axle 2 to constitute a stress measuringdevice, the stress sensors S of many sensor elements effect sensing todeliver stress signals corresponding to shearing strains produced inthree directions, the X-, Y- and Z-axis directions, in the axle 2, andselected out of said stress signals are those stress signals in the X-,Y- and Z-axis directions which are optimum for use as brake controlparameters to enable measurement of the friction force F, vertical loadN and transverse force. Furthermore, stresses in particular directionscan be measured, namely their directions and values can be measured bysorted stress signals in the X- and Y-axis or X-, Y- and Z-axisdirections, and the optimum road surface friction coefficient μ can beeasily obtained by arithmetically processing the selected friction forceF and vertical load N.

In the case where the 1-, 2- or 3-direction stress composite sensor P isselected to constitute a stress measuring device, the 2-direction stresscomposite sensor P2, as shown in FIG. 15, may be installed in the hole 3in the axle to selectively measure stress signals in the X- or Z-axisdirection, or as shown in FIG. 16, the 1- and 2-direction stresscomposite sensors P1 and P2 may be installed in the hole 3 in the axlewith a distance therebetween so that the 1-direction stress compositesensor P1 is used to measure the friction force F which is associatedwith stress signals in the X-axis direction alone, while the 2-directionstress composite sensor P2 is used to measure the load surface frictioncoefficient μ. Alternatively, as shown in FIG. 17, a 3-direction stresscomposite sensor P3 may be installed in the hole 3 in the axle toseparately or selectively use all or some of the stress signals in theX-, Y- and Z-axis directions so as to measure all or some of thefriction force F, vertical load N and transverse force. Thus, 1-, 2- and3-direction stress composite sensors P1, p2 and P3 may be used singly orin combination to constitute stress measuring means for obtaining stresssignals. Stress composite sensors each obtained by forming into a singlepackage a plurality of stress sensors capable of measuring stresses inone direction or a plurality of directions may be used singly or incombination to effect sensing by stress sensors of a plurality ofselected sensor segments alone in the X-axis, X- and Y-axis and X-, Y-and Z-axis directions of the structure, the resulting stress signalsbeing separated according to the X-, Y- and Z-axis directions, and theseparated stress signals are respectively added to provide additionstress signals which are then used for comparative computation.

In addition, the hole 3 in the axle may not necessarily be circular; itmay be polygonal as shown in FIG. 18, in which case the contact betweenthe stress composite sensor and the peripheral wall of the polygonalhole becomes more intimate, facilitating transfer of shearing strainsproduced in the axle to the stress composite sensor, ensuring accuratemeasurement of stresses.

In addition, in the case where a stress composite sensor P is formedinto a small-sized single package, as shown in FIG. 19, the stresscomposite sensor P is inserted in the hole 3 in the axle and fixedtherein by charging filler H such as epoxy resin into the empty space,thus constituting a waterproof stress measuring device. Further, a hole3 of different shape may be formed and a stress composite sensor P maybe embedded in said hole in any desired posture to make it possible tomeasure stresses in a selected direction.

Embodiments in which the stress composite sensor of the presentinvention is embedded in an axle of a vehicle have been described sofar; however, the same functions and effects can be obtained when it isembedded in a strut portion of a vehicle. Further, the invention is notlimited to vehicles and is applicable to other structures.

According to the present invention, a stress composite sensor formeasuring 1-dimensional, 2-dimensional and 3-dimensional stressdirections and stress values can be realized by a single sensor, andwhen this stress composite sensor is embedded in a structure where2-dimensionally or 3-dimensionally complicated stresses occur, necessarystress directions and stress values can be measured.

Particularly, if the stress composite sensor according to the inventionis applied to an axle where 3-dimensionally complicated stresses occur,it is possible to measure selected stresses not influenced by crosstalks; thus, a highly safe brake control system can be provided.

What is claimed is:
 1. A stress composite sensor comprising:sensorelements each including:a base plate having a rectangular configurationand a first main surface and a second main surface opposite said firstmain surface; a pair of first strain gauges disposed on said first mainsurface crossing one another; a pair second strain gauges disposed on asaid second main surface crossing one another; said first pair of straingauges and said second pair of strain gauges being symmetricallydisposed with respect to a center plane of said base plate; and bridgecircuits incorporating said first pair of strain gauges and said secondpair of strain gauges; said sensor elements including X-sensor elementsfor measuring stress in an X-direction and Y-sensor elements formeasuring stress in a Y-direction orthogonal to said X-direction;arithmetic circuits for calculating stress from outputs of said bridgecircuits incorporating said first pair of strain gauges and said secondpair of strain gauges; said sensor elements being substantiallyidentical to each other with respect to size of said base plates anddisposition of said first and second pairs of strain gauges; saidX-sensor elements having edge portions orthogonally joined to edgeportions of said Y-sensor elements to form L-shaped sensor segmentsoutputting X and Y-direction stress signals; and said L-shaped sensorsegments being edgewise joined together in a matrix to form oneassembled body.
 2. The stress composite sensor according to claim 1,wherein said sensor elements include Z-sensor elements for measuringstress in a Z-direction orthogonal to both said X-direction and saidY-direction, said Z-sensor elements each being edgewise join to ones ofsaid L-shaped sensor segments orthogonal to said X-sensor elements andsaid Y-sensor elements thereby forming three contiguous faces of aparallelepiped and outputting X-, Y- and Z-direction stress signals. 3.The stress composite sensor according to claim 1, further comprising:asignal processing circuit for processing outputs of said arithmeticcircuits of said sensor elements to output said X- and Y-directionstress signals; and said bridge circuits including amplifying circuitsintegrally formed on respective ones of said base plates with saidbridge circuits.
 4. The stress composite sensor according to claim 1 incombination with a structural element of a structure, comprising:saidstructural element defining a hole in a stress concentration region ofthe structural element; and said stress composite sensor being imbeddedin said hole at a predetermined orientation relative to said structuralelement for measuring shearing stress in the X-and Y-directions.
 5. Thecombination of claim 4, wherein at least one or more of said sensorelements or said L-shaped sensor segments are selected for stressmeasurement.
 6. The stress composite sensor according to claim 1 incombination with a structural element of a structure, comprising:saidstructural element defining a hole in a stress concentration region ofthe structural element; said stress composite sensor being imbedded insaid hole at a predetermined orientation relative to said structuralelement for measuring shearing stress in the X- and Y-directions; andsaid arithmetic circuits including summing circuits summing respectivelysaid X- and Y-direction stress signals of said L-shaped sensor segments.7. The combination according to claim 6 further comprising means foreffecting comparative computation using said X- and Y-direction summedstress signals of said L-shaped sensor segments.
 8. The combination ofclaim 7, wherein said stress composite sensor is disposed in said holesuch that a plurality of said L-shaped sensor segments are disposed in astress layer having substantially minimized mixing of stresses producedin the structure, and said arithmetic circuits select X-direction andY-direction stress signals from said plurality of said L-shaped sensorsegments and respectively combine said X-direction and Y-directionstress signals.
 9. The combination of claim 7, wherein stresses in the Xand Y-directions are selected to measure stress in a plurality ofdirections, the resulting stress signals being used as controlparameters.
 10. A stress composite sensor comprising:sensor elementseach including:a base plate having a rectangular configuration and afirst main surface and a second main surface opposite said first mainsurface; a pair of first strain gauges disposed on said first mainsurface crossing one another; a pair second strain gauges disposed on asaid second main surface crossing one another; said first pair of straingauges and said second pair of strain gauges being symmetricallydisposed with respect to a center plane of said base plate; and bridgecircuits incorporating said first pair of strain gauges and said secondpair of strain gauges; said sensor elements including X-sensor elementsfor measuring stress in an X-direction, Y-sensor elements for measuringstress in a Y-direction orthogonal to said X-direction, and Z-sensorelements for measuring stress in a Z-direction orthogonal to both saidX-direction and said Y-direction; arithmetic circuits for calculatingstress from outputs of said bridge circuits incorporating said firstpair of strain gauges and said second pair of strain gauges; said sensorelements being substantially identical to each other with respect tosize of said base plates and disposition of said first and second pairsof strain gauges; said X-sensor elements having edge portionsorthogonally joined to edge portions of said Y-sensor elements to formL-shaped sensor segments; said Z-sensor elements each being edgewisejoin to ones of said L-shaped sensor segments orthogonal to saidX-sensor elements and said Y-sensor elements thereby forming three planesensor segments having three contiguous faces of a parallelepiped tooutput X-, Y- and Z-direction stress signals; and said three planesensor segments being joined together in a matrix to form one assembledbody.
 11. The stress composite sensor according to claim 10, furthercomprising:a signal processing circuit for processing outputs of saidarithmetic circuits of said sensor elements to output said X-, Y- andZ-direction stress signals; and said bridge circuits includingamplifying circuits integrally formed on respective ones of said baseplates with said bridge circuits.
 12. The stress composite sensoraccording to claim 10 in combination with a structural elementcomprising:said structural element defining a hole in a stressconcentration region of the structural element; and said stresscomposite sensor being imbedded in said hole at a predeterminedorientation relative to said structural element for measuring shearingstress in the X-, Y- and Z-directions.
 13. The combination of claim 12,wherein at least one or more of said sensor elements or said three planesensor segments are selected for stress measurement.
 14. The stresscomposite sensor according to claim 10 in combination with a structuralelement of a structure, comprising:said structural element defining ahole in a stress concentration region of the structural element; saidstress composite sensor being imbedded in said hole at a predeterminedorientation relative to said structural element for measuring shearingstress in the X-, Y- and Z-directions; and said arithmetic circuitsincluding summing circuits summing respectively said X-, Y- andZ-direction stress signals of said three plane sensor segments.
 15. Thecombination according to claim 14 further comprising means for effectingcomparative computation using said X-, Y- and Z-direction summed stresssignals of said three plane sensor segments.
 16. The combination ofclaim 14, wherein said stress composite sensor is disposed in said holesuch that a plurality of said three plane sensor segments are disposedin a stress layer having substantially minimized mixing of stressesproduced in the structure, and said arithmetic circuits selectX-direction, Y-direction, and Z-direction stress signals from saidplurality of said three plane sensor segments and respectively combinesaid X-direction, Y-direction, and Z-direction stress signals.
 17. Thecombination of claim 14, wherein stresses in the X-direction,Y-direction, and Z-direction are selected to measure stress in aplurality of directions, the resulting stress signals being used ascontrol parameters.